OTTAWA (Reuters) - A huge 19 square mile (55 square km) ice shelf in
Canada's northern Arctic broke away last month and the remaining
shelves have shrunk at a "massive and disturbing" rate, the latest sign
of accelerating climate change in the remote region, scientists said on
Tuesday.

They said the Markham Ice Shelf, one of just five remaining ice
shelves in the Canadian Arctic, split away from Ellesmere Island in
early August. They also said two large chunks totaling 47 square miles
had broken off the nearby Serson Ice Shelf, reducing it in size by 60
percent.

"The changes ... were massive and disturbing," said Warwick Vincent,
director of the Centre for Northern Studies at Laval University in
Quebec.

Temperatures in large parts of the Arctic have risen far faster than
the global average in recent decades, a development that experts say is
linked to global warming.

"These substantial calving events underscore the rapidity of changes
taking place in the Arctic," said Derek Mueller, an Arctic ice shelf
specialist at Trent University in Ontario.

"These changes are irreversible under the present climate and
indicate that the environmental conditions that have kept these ice
shelves in balance for thousands of years are no longer present," he
said in an e-mailed statement from the research team sent late on
Tuesday.

Mueller said the total amount of ice lost from the shelves along
Ellesmere Island this summer totaled 83 square miles -- more than three
times the area of Manhattan island.

The figure is more than 10 times the amount of ice shelf cover that
scientists estimated on July 30 would vanish from around the island
this summer.

"Reduced sea ice conditions and unusually high air temperatures have
facilitated the ice shelf losses," said Luke Copland of the University
of Ottawa.

BLEAK FUTURE

"Extensive new cracks across remaining parts of the largest
remaining ice shelf, the Ward Hunt, mean that it will continue to
disintegrate in the coming years," he said.

The first sign of serious recent erosion in the five shelves came in
late July, when sheets of ice totaling almost eight square miles broke
off the Ward Hunt shelf. Since then that shelf has lost another 8.5
square miles.

Ellesmere Island was once home to a single enormous ice shelf
totaling around 3,500 square miles. All that is left of that shelf
today are the four much smaller shelves that together cover little more
than 300 square miles.

Scientists say the ice shelves, which contain unique ecosystems that
had yet to be studied, will not be replaced because they took so long
to form.

The rapid melting of ice in the Canadian Arctic archipelago worries
Ottawa, which fears foreign ships might try to sail through the waters
without seeking permission first.

Last week Prime Minister Stephen Harper said Canada would toughen
reporting requirements for ships entering its waters in the Far North,
where some of those territorial claims are disputed by the United
States and other countries.